1. Field of the Invention
The present invention relates generally to machine tools such as milling machines and more particularly pertains to feeding apparatus for feeding or moving a workpiece or a movable member such as a work-table holding a workpiece to a desired position in machine tools.
2. Description of the Prior Art
In machine tools such as milling machines, it is necessary to feed or bring a workpiece to be processed to a desired position with regard to a processing tool such as a milling cutter. Particularly in the milling machines, it is necessary to vertically move a work-table holding a workpiece to a milling cutter mounted above the work-table so that the workpiece may be fed into engagement with the milling cutter.
Stated further using milling machines as an example, the work-table holding the workpiece is conventionally so arranged as to be vertically moved by means of a lead screw which is manually rotatable by means of a handwheel or a crank. Also, in order to easily move the work-table, the lead screw for moving the work-table is so arranged as to be rotated alternatively either manually by means of the handwheel or crank or by power in well-developed milling machines. In this arrangement, the lead screw is rotated by power to rapidly bring the work-table near to the milling cutter and it is rotated manually by the handwheel or crank to adjustably feed the workpiece into engagement with the milling cutter.
In the milling machines in which the lead screw for moving the work-table is rotatable manually and by power, the trouble has been that the handwheel or the lever will be often unintentionally rotated when the work-table is to be vertically moved by power. Also, it has been often found that the handwheel or the lever will be unintentionally rotated by power when it is being manually rotated by hand to adjustably feed the workpiece to the milling cutter. Of course, there is a danger of injuring the operator or the milling machine if the handwheel or the lever is unintentionally rotated, especially since it will be rapidly rotated by power. Such unintentional rotation or movement of operating members has been found with regard to other machine tools than the milling machines having feeding apparatus which are arranged more or less in the same manner as the milling machines.